A semiconductor device that utilizes a semiconductor material such as silicon or a nitride semiconductor material (group 13 nitride (AlN, GaN, or InN) or a mixed crystal thereof) that forms a PN junction has been widely put to practical use. A semiconductor device has been generally produced on an expensive single-crystal substrate (e.g., sapphire or silicon carbide) by a method with low mass productivity. Therefore, such an expensive semiconductor device has been used as a point light source instead of a surface light source.
An organic EL device has been known as a surface light source (see Non-patent Document 1, for example). Since the organic EL device can be produced using an inexpensive plastic substrate or glass, the organic EL device is inexpensive, and can be used as a surface light source. The organic EL device is expected to be used as a flexible light-emitting device or illumination device.
It has been proposed to form a semiconductor layer on a graphite substrate that exhibits heat resistance, and exhibits flexibility when an external force is applied. A graphite film that is obtained by heating a polymer (e.g., polyimide or POD) at a high temperature and has c-axis orientation has been proposed as the graphite substrate.